PV Gap

Stella Said:

how do i find the internal resistance of a solar cell?

We Answered:

Connect a resistor bank in series to your solar cell and a voltmeter parallel to your resistor bank. Vary the resistance and record it with its corresponding voltage reading. Assuming the Solar cell is a current source, its internal resistance would be equal to its load resistance when maximum power is delivered to your resistor. To get maximum power delivered by your solar cell to the resistor, plot power (P=[V^2]/[R]) against resistance R. Look for the point where Power is highest and you have maximum power. It's corresponding resistance should be the resistance for maximum power and therefore it would be more or less equal to the solar cell's internal resistance.

Jeanne Said:

Solar Cell Resistance/Circuit Question?

We Answered:

1) low voltage, high current devices <=== parallel
2) high voltage, low current devices <=== series


with parallel suppplies, voltage is identical across each
supply while current is the arithmetic sum of the paralllel
cells' current


with series supplies, the voltage = sum of in-line
voltages while current is limited by the lowest current
device in the chain.

Phyllis Said:

How does the short circuit voltage and short circuit current of solar cell varies with the light intensity?

We Answered:

Hello Gopinath...Have you ever looked on the back of your solar panel its got some blipvert on it that describes the max voltage and the max current at a shorted level ... If you think about it though everything that the chart relates to you is relative to the amount of insolation http://en.wikipedia.org/wiki/Insolation you have in your area ..I mean if you don't have the watt/meter^3 the chart is wrong...You hav To check what you have where you are that's the practical approach...From a purely hypothetical standpoint they both are directly proportional to the amount of light you have. Less light less voltage less voltage higher current draw given same work...That's why I recommend the thermal breakers on every panel so you don't just overwork the top three or the like...Quick story here I bought an Omron Plc on ebay for 125 buck and the program sysmac for may ladder logic and set the whole thing up on a monitored output so if it exceeds 45% it cuts itself off it only took one 7point IO rack and some 30 or 40 lines of code...the whole package was less than 200 dollars...not for everyone but it watches when I can't.... There ya go from the E

Marshall Said:

what causes a solar cell to create current around a circuit?

We Answered:

The solar cell works in three steps:
1. Photons in sunlight hit the solar panel and are absorbed by semiconducting materials, such as silicon.
2. Electrons (negatively charged) are knocked loose from their atoms, allowing them to flow through the material to produce electricity. Due to the special composition of solar cells, the electrons are only allowed to move in a single direction.
3. An array of solar cells converts solar energy into a usable amount of direct current (DC) electricity.

When a photon is absorbed, its energy is given to an electron in the crystal lattice. Usually this electron is in the valence band, and is tightly bound in covalent bonds between neighboring atoms, and hence unable to move far. The energy given to it by the photon "excites" it into the conduction band, where it is free to move around within the semiconductor. The covalent bond that the electron was previously a part of now has one fewer electron — this is known as a hole. The presence of a missing covalent bond allows the bonded electrons of neighboring atoms to move into the "hole," leaving another hole behind, and in this way a hole can move through the lattice. Thus, it can be said that photons absorbed in the semiconductor create mobile electron-hole pairs.

Ohmic metal-semiconductor contacts are made to both the n-type and p-type sides of the solar cell, and the electrodes connected to an external load. Electrons that are created on the n-type side, or have been "collected" by the junction and swept onto the n-type side, may travel through the wire, power the load, and continue through the wire until they reach the p-type semiconductor-metal contact. Here, they recombine with a hole that was either created as an electron-hole pair on the p-type side of the solar cell, or a hole that was swept across the junction from the n-type side after being created there.

Alexander Said:

Is there a special way to connect an amp meter with a volt meter to a solar cell in a parrallel circuit?

We Answered:

you need a load, such as a power resistor of the proper size, as i said in your other similar question. Then put the ammeter in series with the load, and the voltmeter across it.

If you just want to see if it is working, get a value of resistor equal to the rated voltage divided by the rated current. Get a power resistor of enough power to handle the rated power of the array.